Then create a batch file on the same file share like name it installagent.bat or something like that. Installing agent now consists of just navigating to the file share and running the batch file, from each windows box.

I've made my own version of the install script originally posted here.
This script stops the service, uninstalls the agent and then installs and starts the new version of the agent from the server. It also adds a firewall rule (windows 7 / server 2008) and has a little more sophisticated way of telling the architecture.

An install directory is also made an option and it supports installs with proxy as well.

:RemoveService
ECHO.
REM Change working directory and partition and create InstallDir if it does not exist
if not exist %SystemDrive%\%InstallDir%\. mkdir %SystemDrive%\%InstallDir%
CD %SystemDrive%\%InstallDir%
%SystemDrive%

:InstallService
ECHO.
REM Change working directory and partition and create InstallDir if it does not exist
if not exist %SystemDrive%\%InstallDir%\. mkdir %SystemDrive%\%InstallDir%
CD %SystemDrive%\%InstallDir%
%SystemDrive%

1) First i detect if its a reinstall of a new install.
2) Then I check if its a 32 of 64 bit machine.
3) Then we ask how the machine is called in Zabbix
4) Then we ask which proxy is going to monitor the machine.
5) Then we check if the zabbix server is able to connect to the agent. (agent.php on the zabbix server)